عنوان مقاله [English]
In this paper, a homogeneous isotropic turbulent flow inside a box with periodic boundary conditions laden with heavy spherical particles is investigated. The mixed stick-slip boundary condition is applied onto the particles surface. In all previous studies, the problem have been solved by considering no-slip boundary condition on the particles, but this assumption is not always acceptable, e.g., in two-phase liquid-liquid and liquid-gas suspensions. For example, assuming no-slip boundary condition on the surface of
liquid particles is not realistic, because, the background flow induces a flow inside the liquid drops, and thus, there is a non-zero velocity at the interface. This effect can be modeled by assuming the slip boundary condition. Furthermore, due to the evaporation of liquid particles suspended in a gas, there is a mass transfer at the interface, which could be modeled as a boundary slip, again. Also, with the progress of technology, hydrophobic materials are being used in various areas. These surfaces cause an apparent slip at the boundary. Hence, the study of mixed stick-slip boundary condition is of great fundamental as well as applied importance, because the effect of creeping flow boundary condition on the dynamics of the particles can be observed. The background turbulent flow field is computed using the direct numerical simulation (DNS) technique. In order to sustain the turbulence state, a linear forcing scheme is employed. The particle dynamics is governed by the Maxey-Riley equation. The drag force acting on the particle is obtained by solving creeping flow around a spherical particle with slip boundary condition. The so-obtained analytical formula for the drag force is supplied to the DNS solver. Simulations were conducted with different number of particles, different Stokes numbers, and different amounts of slippage. Results show that the increase of the slip on the particles surface causes the decrease of the preferential concentration. By using Q criterion, the vortices are detected and behaviors of particles near these vortices are studied. Results show that by decreasing Trostel number and drag force, particles run away more quickly from the vortices.